In wireless communication networks it is common practice to establish mobile terminating transactions, e.g., calls or SMS transactions, by paging the terminating mobiles via a network node, e.g., a mobile switching center MSC.
Generally, to establish the mobile terminating transactions, the network node will receive a first number of paging messages for establishment of communication transactions. In view of the operative state of paging areas in the wireless communication network, the network node will forward a subset of a number of paging messages from the received paging messages to at least one paging area in the wireless communication network for subsequent broadcasting thereof to the terminating mobile terminal. In other words, the network node controls a paging admission rate, which paging admission rate is the ratio between the number of paging messages forwarded to the wireless communication network and the number of paging messages received at the network node. It should be understood that the paging admission rate is a control parameter which varies during operation of the network node.
Also, as a further control parameter for the operation of the network node there is considered a so-called paging success rate as ratio between paging messages successfully broadcast to a paging area in the wireless communication network and the number of paging messages forwarded from the network node to the paging area.
FIG. 1 shows a flowchart of operation for a usual paging flow control method.
As shown in FIG. 1, in the operation of the network node there are used further parameters of control, e.g., an upper paging success rate limit and a lower paging success rate limit.
As shown in FIG. 1, in the network node there will be periodically calculated the paging success rate for ongoing paging message transactions, e.g., every thirty seconds. Then, the determined paging success rate will be compared both to the upper paging success rate limit and to the lower paging success rate limit. Assuming that the paging success rate is larger than the upper paging success rate limit, this will be an indication that it is possible to increase the paging admission rate. If the paging success rate is lying between the upper paging success rate limit and the lower paging success rate limit, then it is appropriate to maintain the paging admission rate unchanged. If the paging success rate is lower than or equal to a lower paging success rate limit, then this is an indication of overload in the wireless communication network, and a decrease of the paging admission rate will be achieved so as to maintain a certain success rate level for ongoing paging message transactions.
As shown in FIG. 1, from the paging success rate the network node decides whether a paging area is working normally or in an overload situation. Here, an overload situation means that base station controllers BSC/radio network controllers RNC serving one or more paging areas are in an overload situation.
As shown in FIG. 1, in case of an overload situation, the network node reduces step by step the number of paging attempts done to the respective paging area, until the paging success rate for the overloaded paging area improves again. Then, the network node increases again the paging admission rate until the paging success rate stabilizes.
As shown in FIG. 1, to decrease/increase the number of paging attempts, the network node uses the paging admission rate which directly depends on the paging success rate. When the paging admission rate is at the highest level, no restriction for paging message transactions is executed, which is the normal traffic scenario when a paging success rate is 100%. Otherwise, when the paging admission rate is at the minimum level, a maximum restriction of 100% is executed, and no paging message transactions are performed any more. Otherwise, for paging admission rates lying between the maximum and the minimum values, more or less paging message transactions will be suppressed.
FIG. 2 shows an operative scenario for the wireless communication network, where the paging control process illustrated with respect to FIG. 1 leads to problems.
As shown in FIG. 2, one may assume without loss of generality that the network node, e.g., the mobile switching center MSC, is connected to two different radio network controllers RNC1, RNC2, where the second radio network controller RNC2 is again connected to a plurality of base stations BS1, BS2, and BS3. Again, without loss of generality, one may assume that only the first two base stations BS1 and BS2 are in the operative mode, while the third base station BS3 is out of operative order. In other words, FIG. 2 illustrates an operative scenario for the wireless communication network, where only two thirds of paging areas are reachable at a specific time of operation.
Further, one may consider an operative condition wherein the network node receives a constant number of, e.g., 1,000 paging messages over several paging control intervals, e.g., thirty seconds. During normal operation, as there is no overload situation, all 1,000 paging message transactions will be processed successfully. Now assuming that the third base station BS3 shown in FIG. 2 goes out of operation, e.g., according to a disaster like an earthquake, only 66% of the base stations will be reachable, e.g., the base station BS1 and the base station BS2, and will be able to handle 66% of the 1,000 paging messages forwarded by the network node MSC.
Further, the paging flow control process executed in the network node MSC will determine a paging success rate of 66%. Assuming that, e.g., the lower paging success rate limit referred to in FIG. 1 set to 75%, the paging flow control process executed by the network node will accordingly start to decrease the paging admission rate, e.g., to a value of 80%. The consequence thereof will be that from the network node MSC, only 800 paging request transactions will be initiated towards the wireless communication network in the next control period. However, as still only 66% of the paging area is reachable, only 528 paging message transactions will be successful. Therefore, the paging flow control process executed in the network node MSC will still see only a success rate of 66% and will therefore again reduce the paging admission rate until finally all paging message transactions are stopped.
From the above, the problem existing with usual paging flow control solutions is that the paging flow control process will regulate down the paging admission rate to zero, if the paging success rate is continuously below the lower paging success rate limit. In other words, even if part of the wireless communication network is operative to handle a certain amount of paging message transactions, nevertheless, this part of the wireless communication network will not be used for paging message transactions due to a static coupling between the paging success rate and the lower paging success rate limit during paging flow control.